The present invention relates to a shaft sealing assembly that is used in a refrigerant compressor installed in a refrigeration circuit and seals a rotary shaft of the compressor with a lip seal.
In such a shaft sealing assembly, the internal pressure of a refrigerant compressor acts on a lip portion of the lip seal. The force with which the lip portion is pressed against the rotary shaft is adjusted in accordance with the internal pressure. This is referred to as “self-sealing” function. However, an excessively high internal pressure excessively increases the pressing force of the lip portion applied to the rotary shaft, which causes the lip portion to be abnormally worn.
To prevent the abnormal wear, Japanese Laid-Open Patent Publication No. 2002-71028 discloses a configuration in which a space surrounding the back of a lip portion is filled with an annular elastic member. The elastic member receives an excessive internal pressure of a refrigerant compressor and prevents the excessive pressure from acting on the back of the lip portion. Therefore, the pressing force of the lip portion acting on the rotary shaft is prevented from being excessive, and the lip portion is prevented from being abnormally worn. Accordingly, the durability of the lip portion is improved.
However, the elastic member reduces the flexibility of the lip portion and thus prevents the lip portion from readily following displacement of the rotary shaft. This lowers the effectiveness of the lip seal.
The above-mentioned publication recites that the elastic member is made of a material that is softer than the lip portion, so that the property of the lip portion to follow displacement of the rotary shaft is maintained. However, even if a material that is softer than that of the lip portion is used for the elastic member, filling the space surrounding the back of the lip portion with the elastic member lowers the flexibility of the lip portion compared to a case where the space is not filled with any member. Therefore, the sealing assembly of the above mentioned publication can hardly improve the durability of the lip portion and maintain a satisfactory property of the lip portion to follow displacement of the rotary shaft at the same time.